HS2: Should it have been a single tunnel?

[The_Emperor]

Mod Note: Posts #1 - #8 originally in this thread.

I know it is 4x more expensive to build a tunnel than go overground, but HS2 has already tripled in budget and shrunk in scope so I’m going to ask the question. If we could go back, would it be cheaper to build a single tunnel given the fixed cost nature of a tunnelling project? I want an underground tunnel between Liverpool, Manchester and Leeds.

 

[Bald Rick]

If we could go back, would it be cheaper to build a single tunnel given the fixed cost nature of a tunnelling project?

What do you mean by ‘single tunnel’ ?

 

[LNW-GW Joint]

I know it is 4x more expensive to build a tunnel than go overground, but HS2 has already tripled in budget and shrunk in scope so I’m going to ask the question. If we could go back, would it be cheaper to build a single tunnel given the fixed cost nature of a tunnelling project? I want an underground tunnel between Liverpool, Manchester and Leeds.

I don't think HS2 Ltd would agree that Phase 1 and 2a (the sections that have parliamentary approval and are under construction) have been descoped or are over budget.
Though there are cost pressures, not least inflation of supplies and labour.
Later phases are still being argued about and are not set in stone, but most of the eastern leg has gone as well as the Golborne link.
The Bill for Phase 2b West (Crewe-Manchester) is proceeding through parliament at the moment, and may get royal assent about this time next year.
The overall HS2+NPR budget is set at £96 billion (that's spend from I think 1.4.22 on both projects, including the current TRU project).

Plans for NPR between Liverpool, Manchester and Leeds are extremely vague and there have been contradictory statements from government sources.
A new Pennine tunnel may or may not be in the mix (possibly Guide Bridge-Marsden, but who knows).
It's simply too early to say how any new line will be routed and built.
This week's statements say that Bradford must have a better solution, which further complicates matters.

I think the Phase 1 tunnels are on quite tight contracts, as the task is relatively well defined and costed, with the TBMs mostly built and crews recruited.
So the cost pressures fall on the contractors, at least initially.
The railway contracts (track, OHLE, signalling etc) will also be quite tightly set, but they haven't been let yet so costs are not fixed.
A Pennine tunnel would be a different animal, boring through all that unstable millstone grit - ask the builders of Summit/Woodhead/Standedge and the rest.

 

[Bald Rick]

A new Pennine tunnel may or may not be in the mix (possibly Guide Bridge-Marsden, but who knows).

It’s Ardwick - Marsden (coming up for air briefly along the way), as has been said several times

A Pennine tunnel would be a different animal, boring through all that unstable millstone grit

true.

 

[LNW-GW Joint]

It’s Ardwick - Marsden (coming up for air briefly along the way), as has been said several times

I thought Shapps (in his new job, not as Transport SoS) had poured cold water on a "new Pennine tunnel" when there were spare ones there already?
That looked like trying to avoid at least some of the Marsden tunnel.
And it all has to cost no more than £96 billion (or whatever cap is left after HS2 reaches Piccadilly).

 

[CardiffKid]

I know it is 4x more expensive to build a tunnel than go overground, but HS2 has already tripled in budget and shrunk in scope so I’m going to ask the question. If we could go back, would it be cheaper to build a single tunnel given the fixed cost nature of a tunnelling project? I want an underground tunnel between Liverpool, Manchester and Leeds.

If you mean one single tunnel between London and Birmingham, no it would be prohibitively more expensive and time consuming.

Costs would also increase/over run and of course be logistically more complicated.

 

[snowball]

I thought Shapps (in his new job, not as Transport SoS) had poured cold water on a "new Pennine tunnel" when there were spare ones there already?

I think that was in the earliest days of Sunak's PM-ship, before the mid-November financial statement which clarified the Sunak/Hunt position on the IRP, and Shapps was arguing against the Truss-style maximalist NPR route via Bradford.

 

[LNW-GW Joint]

I think that was in the earliest days of Sunak's PM-ship, before the mid-November financial statement which clarified the Sunak/Hunt position on the IRP, and Shapps was arguing against the Truss-style maximalist NPR route via Bradford.

Yes I'm sure you are right there.
Shapps still sometimes pops up as some kind of government spokesman, but I doubt he will keep up with the detail of how NPR unfolds.
Nevertheless, if they can cancel HS2 East and the Golborne link, no new line is certain until the Bill gets through parliament.
Crewe-Manchester has still to get through the parliamentary mincer, while costs rise inexorably on Phases 1/2a.

 

[HSTEd]

It is obviously difficult to make sweeping statements about the relative costs of schemes as large as complex as HS2.

But given the runaway growth in costs and the political rancour that it has generated, a more tunneled scheme would have some advantages......

Tunnels are becoming comparatively cheaper all the time, see the Woodsmith Tunnel being built simply to make planning easier to obtain.

Such a thing would have been unthinkable as an option in the past.
Utility relocations, fighting everyone and political rancour over protests are no small issue.

I think pretty much every major modification to the proposed scheme has added more tunnel......

EDIT:

Would be interesting to see whether you could do the Barcelona Metro thing and dig the tunnel as a single bore with two isolated decks holding one track each, which would provide the requisite fire isolation. Would allow you to leverage really large TBMs. Also it would provide a lot of extra volume inside the bores to reduce the extra costs with evacuation points.

 

[Bald Rick]

Such a thing would have been unthinkable as an option in the past.

Plenty of examples of tunnels in the 1800s to avoid difficulties with landowners (effectively the precursor to planning law). Shugborough for example.

Anyway, the big cost in tunnelling with TBMs is not TBMs, it is volume, both in terms of material out (and disposal thereof) and material in. A single tunnel with two tracks is a lot more voluminous than two twin bores. And therefore more expensive.

 

[Nottingham59]

I'm convinced it would have been much better to have built HS2 in a tunnel directly from Euston to Tring, merging onto the WCML fast lines between Tring and Cheddington. Cost = £2bn for Euston station and £7.8bn for the tunnels, assuming £100M/km for 2x30km of bored tunnel and £50M/km for 2x18km of cut-and-cover. Much cheaper than going the long way round via Old Oak Common which is actually to the south of Euston.

Phase 2 could then have run over open country between Tring and Rugby, teminating with three spurs towards Birmingham, Trent Valley, and Leicester. That would have fixed the WCML capacity issue, and left many tens of billions spare to fix the rail networks in and around Birmingham, Manchester and Leeds. These fixes would have included new stations able to take very long trains, cross-city tunnels, and new lines towards London.)

Old Oak Common could have been accessed, if necessary, with terminating platforms off the WCML fast lines. If built first, these could also act as an alternative terminus to simplify the Euston rebuild.

And I would have had 530m platforms at Euston, so that half-length trains (265m) would have made much more efficient use of existing platforms in Glasgow, Edinburgh, Liverpool, Leicester, Nottingham, Sheffield, York, Newcastle etc., where their flagship London services will in future be constrained to just 200m under HS2.

EDIT: NB. The tunneling costs above are for the civils only.

 

[Bald Rick]

I'm convinced it would have been much better to have built HS2 in a tunnel directly from Euston to Tring, merging onto the WCML fast lines between Tring and Cheddington. Cost = £2bn for Euston station and £7.8bn for the tunnels, assuming £100M/km for 2x30km of bored tunnel and £50M/km for 2x18km of cut-and-cover. Much cheaper than going the long way round via Old Oak Common which is actually to the south of Euston.

Phase 2 could then have run over open country between Tring and Rugby, teminating with three spurs towards Birmingham, Trent Valley, and Leicester. That would have fixed the WCML capacity issue, and left many tens of billions spare to fix the rail networks in and around Birmingham, Manchester and Leeds. These fixes would have included new stations able to take very long trains, cross-city tunnels, and new lines towards London.)

all sorts of options like this were considered, and rejected for not being as good value for money.

and your proposal only ‘fixes’ the capacity issue on the WCML south, but does nothing for the Coventry corridor, New St approaches, Crewe, or the Manchester approaches.

Also your costs are out. A lot!

 

[Killingworth]

Mod Note: Posts #1 - #8 originally in this thread.

I know it is 4x more expensive to build a tunnel than go overground, but HS2 has already tripled in budget and shrunk in scope so I’m going to ask the question. If we could go back, would it be cheaper to build a single tunnel given the fixed cost nature of a tunnelling project? I want an underground tunnel between Liverpool, Manchester and Leeds.

Can we add in Sheffield please while we're at it, to Leeds and Manchester?

 

[Nottingham59]

Coventry corridor, New St approaches, Crewe, or the Manchester approaches.

New St approaches and Manchester approaches are exactly what I mean by "new lines towards London".

Also your costs are out. A lot!

I'm merely quoting the expert...

Fantasy tunnelling suggestions

Tunnels shape a railway network for the next hundred years. Once built, they are fixed and the rest of the network has to evolve around them; their size limits the loading gauge of the line in perpetuity. So where would you put them? This is the deal: You are in charge of a fully-funded...

www.railforums.co.uk

"Put all that together and you have costs of, very approximately:

£300m fixed + £100m/km, at today’s price base."

- Bald Rick, 29 June 2022

 

[Bald Rick]

I'm merely quoting the expert...

Yeah, what does he know

(I walked right into that)

 

[D365]

one continuous tunnel would require a substantial number of emergency access points. Easier to just surface the line now and again.

 

[Xavi]

I thought Shapps (in his new job, not as Transport SoS) had poured cold water on a "new Pennine tunnel" when there were spare ones there already?
That looked like trying to avoid at least some of the Marsden tunnel.
And it all has to cost no more than £96 billion (or whatever cap is left after HS2 reaches Piccadilly).

Procurement for development work on the Warrington to Marsden (including tunnels) NPR has commenced. It’s not part of the HS2 budget.

 

[The Ham]

Plenty of examples of tunnels in the 1800s to avoid difficulties with landowners (effectively the precursor to planning law). Shugborough for example.

Anyway, the big cost in tunnelling with TBMs is not TBMs, it is volume, both in terms of material out (and disposal thereof) and material in. A single tunnel with two tracks is a lot more voluminous than two twin bores. And therefore more expensive.

As a rough rule of thumb as you double the diameter you quadruple the cross sectional area.

As such two tunnels with a given diameter require half the soil disposal of one tunnel twice the size of the two.

Even if you could reduce the diameter to less than 2x it's still got to be 1.5x to be about the same area.

As you get bigger you typically need a thicker lining width to allow for the larger structural strength required.

I don't know about tunnels, however in drainage pipes these get proportionally thicker with size, however this still requires more concrete to create the larger tunnel.

2 pipes of x require concrete of 2, however 1 pipe of 1.5x requires concrete of 2.25., so even if you can match the earth disposal volume you've still likely to need more concrete.

 

[randyrippley]

Mod Note: Posts #1 - #8 originally in this thread.

I know it is 4x more expensive to build a tunnel than go overground, but HS2 has already tripled in budget and shrunk in scope so I’m going to ask the question. If we could go back, would it be cheaper to build a single tunnel given the fixed cost nature of a tunnelling project? I want an underground tunnel between Liverpool, Manchester and Leeds.

building a tunnel under or through the Lancashire / Cheshire mosses could be challenging

== Doublepost prevention - post automatically merged: 21 Jan 2023 ==

As a rough rule of thumb as you double the diameter you quadruple the cross sectional area.

As such two tunnels with a given diameter require half the soil disposal of one tunnel twice the size of the two.

Even if you could reduce the diameter to less than 2x it's still got to be 1.5x to be about the same area.

As you get bigger you typically need a thicker lining width to allow for the larger structural strength required.

I don't know about tunnels, however in drainage pipes these get proportionally thicker with size, however this still requires more concrete to create the larger tunnel.

2 pipes of x require concrete of 2, however 1 pipe of 1.5x requires concrete of 2.25., so even if you can match the earth disposal volume you've still likely to need more concrete.

So we need a rectangular TBM
Theoretically you could do it with rows of rotating drum cutters, but it would need a lot of R&D

 

[6Gman]

I'm convinced it would have been much better to have built HS2 in a tunnel directly from Euston to Tring, merging onto the WCML fast lines between Tring and Cheddington. Cost = £2bn for Euston station and £7.8bn for the tunnels, assuming £100M/km for 2x30km of bored tunnel and £50M/km for 2x18km of cut-and-cover. Much cheaper than going the long way round via Old Oak Common which is actually to the south of Euston.

Phase 2 could then have run over open country between Tring and Rugby, teminating with three spurs towards Birmingham, Trent Valley, and Leicester. That would have fixed the WCML capacity issue, and left many tens of billions spare to fix the rail networks in and around Birmingham, Manchester and Leeds. These fixes would have included new stations able to take very long trains, cross-city tunnels, and new lines towards London.)

Old Oak Common could have been accessed, if necessary, with terminating platforms off the WCML fast lines. If built first, these could also act as an alternative terminus to simplify the Euston rebuild.

And I would have had 530m platforms at Euston, so that half-length trains (265m) would have made much more efficient use of existing platforms in Glasgow, Edinburgh, Liverpool, Leicester, Nottingham, Sheffield, York, Newcastle etc., where their flagship London services will in future be constrained to just 200m under HS2.

EDIT: NB. The tunneling costs above are for the civils only.

That really isn't how it works.

A capital scheme of this nature is justified on its own merits.

Schemes in Birmingham, Manchester, Leeds are justified on their own merits.

There isn't some single pot of money that can be switched from project to project.

 

[Nottingham59]

A capital scheme of this nature is justified on its own merits.

How I wish that were true. Unfortunately, HS2 was not justified on its merits. The BCR of the whole project (phase 1, phase 2a to Crewe and Phase 2b West to Manchester) was 0.7 without the now-dropped Golborne Link, and 0.9 with it. See fig 4 on page 16 and figure A1 on page 21 of this document from July 2022. And to get even those figures they had to ignore the behavioural change from Covid and extend the appraisal period out to 100 years.

HS2 Crewe to Manchester: impacts of removing the Golborne Link

Supplement to the update on the strategic outline business case.

www.gov.uk

 

[D365]

Please let's not turn this into another inane BCR discussion...

 

[Nottingham59]

let's not turn this into another inane BCR discussion

You're right. Let's not

(I walked right into that)

Don't worry about it! I really appreciate your contributions to these discussions. Especially your knowledge about actual costs of infrastructure, which are very difficult to work out any other way.

So we need a rectangular TBM

lol. You can just about fit 2 HS2 trains side by side in a single HS2 tunnel, with its 8.8m internal diameter. See the first post in this thread for a scale diagram. But not passing at speed, of course.

Fantasy tunnelling suggestions

Tunnels shape a railway network for the next hundred years. Once built, they are fixed and the rest of the network has to evolve around them; their size limits the loading gauge of the line in perpetuity. So where would you put them? This is the deal: You are in charge of a fully-funded...

www.railforums.co.uk

 

[LesF]

[B]The_Emperor[/B] - Cheaper to build two single track bored tunnels than one tunnel with twin tracks. That's because the height of the bored tunnel is the same as the width, so there's more excavation than necessary for a twin-track tunnel. No point in building more tunnel than necessary as it's so expensive. HS2 could have reached Birmingham with a quarter of the tunnel length via the M1 route.​

[SIZE=14px]LNW-GW Joint[/SIZE] - NPR will fail if it doesn't have a new Pennine tunnel. That tunnel needs to connect Manchester, Leeds (and Sheffield Mr Killingworth). Only the Woodhead route does that. Easier "boring through all that unstable millstone grit" when you rebore the existing Woodhead Victorian tunnels. Bradford has a simple solution: join the two terminii together.

[B]HSTEd[/B] - the Woodsmith mine tunnel is 23 miles long and is bored through mudstone - much easier than rock. The developer obviously thinks it's worth it to export £12bn worth of potash.​

Nottingham59 - absolutely right that HS2 should have struck northwards instead of doing a rail tour via Old Oak Common.​

HS2 isn't justified on any honest metric. The brief said Design a railway from London to W Midlands and think about where to go next. That isn't the way to design anything. You have to start with an overall plan for the country's railway, then focus on the detail. Otherwise you get what we have now, work started on an ill conceived "plan" that doesn't comply with the brief, will never do what was intended, costs several times what parliament was promised, with unnecessary levels of destruction and disruption.

Please excuse the bold type - can't change it.

 

[HSTEd]

Anyway, the big cost in tunnelling with TBMs is not TBMs, it is volume, both in terms of material out (and disposal thereof) and material in. A single tunnel with two tracks is a lot more voluminous than two twin bores. And therefore more expensive.

I hesitate to go against your expert opinion, but if we go to the HS2 Guide to tunneling costs this is not the impression that that document gives.

Whilst this document is obviously old and inflation will have done a number on the figures presented, the proportions still give an impression.
Of the £491m of the example tunnel, only £31.5m relates to the disposal of spoil, which is the only parameter that will scale simply with excavated volume.

Whilst more spoil will be transported to the tunnel mouth with a larger single bore, less (but bigger) equipment will be necessary to do so since fewer faces will be providing the material.
Fewer tunnel segments will have to be placed, although they will be bigger, fewer pieces of ancillary plant will be required, less non TBM excavation will be required, and fewer staff are required to watch over one TBM than two.

I think the picture is a little more complicated than a simplistic "excavate smallest possible tunnel volume" model.

Indeed in the example I cited, of the Barcelona metro, it was preferred to excavate one giant tunnel bore with a TBM because it allows simplification of other aspects of the project - such as much simpler station or access shaft construction, which is considered to be a greater saving.

If you put the two HS2 tracks inside a double deck big bore tunnel, an emergency evacuation point could be a simple pair of drifts to the surface driven from one side of the tunnel, there would be none of the complex box structures seen in more "conventional" tunnels.

But once again, you are the expert and I am not, so I concede the point.

EDIT:

Additionally, given that tunnel diameters for high speed rail are determined by aerodynamic factors rather than actually fitting equipment inside the tunnel, I'm not sure how much greater the cross-section of the single bore tunnel would even be!

 

[12LDA28C]

with unnecessary levels of destruction and disruption.

in your opinion...

Do you think that (yet another) upgrade of the WCML would have caused less destruction and disruption?

 

[LesF]

12LDA28C - no I don't. The West Coast Route Modernisation in the noughties was largely about catching up on maintenance on existing tracks. Where new tracks were added in the Trent valley, the work went smoothly without disrupting the existing tracks. I was in favour of a HS line following M1 until Covid and WFH rendered it unnecessary for many years. But unpredictable events like Covid and war are no excuse for starting out with an ill-conceived, unworkable plan.​

 

[The Planner]

12LDA28C - no I don't. The West Coast Route Modernisation in the noughties was largely about catching up on maintenance on existing tracks. Where new tracks were added in the Trent valley, the work went smoothly without disrupting the existing tracks. I was in favour of a HS line following M1 until Covid and WFH rendered it unnecessary for many years. But unpredictable events like Covid and war are no excuse for starting out with an ill-conceived, unworkable plan.​

Eh? So a completely remodelled Rugby, improved speeds and signalling was catching up on maintenance?

 

[Bald Rick]

So we need a rectangular TBM

Monsieur Brunel (Senior) found out how much material you need to keep a rectangular bored tunnel in place. Circular (or near circular) bored tunnels are so much more efficient in engineering.

The West Coast Route Modernisation in the noughties was largely about catching up on maintenance on existing tracks. Where new tracks were added in the Trent valley, the work went smoothly without disrupting the existing tracks.

It wasn’t any thing to do with catching up maintenance*, and you must have missed the three years of no weekend services via the Trent Valley and multiple weeks of total blockade.

*There was a lot of renewals done concurrently.

 

[6Gman]

How I wish that were true. Unfortunately, HS2 was not justified on its merits. The BCR of the whole project (phase 1, phase 2a to Crewe and Phase 2b West to Manchester) was 0.7 without the now-dropped Golborne Link, and 0.9 with it. See fig 4 on page 16 and figure A1 on page 21 of this document from July 2022. And to get even those figures they had to ignore the behavioural change from Covid and extend the appraisal period out to 100 years.

HS2 Crewe to Manchester: impacts of removing the Golborne Link

Supplement to the update on the strategic outline business case.

www.gov.uk

View attachment 127472

That may well be the case but it was not the point I was making, which was that cancelling one capital scheme does not mean an equivalent amount is then available for a different project.

== Doublepost prevention - post automatically merged: 21 Jan 2023 ==

12LDA28C - no I don't. The West Coast Route Modernisation in the noughties was largely about catching up on maintenance on existing tracks. Where new tracks were added in the Trent valley, the work went smoothly without disrupting the existing tracks. I was in favour of a HS line following M1 until Covid and WFH rendered it unnecessary for many years. But unpredictable events like Covid and war are no excuse for starting out with an ill-conceived, unworkable plan.​

Weren't there months* of line closures and disruption?


* @Bald Rick reminds me that should be years not months.